Robust Covertness in Joint Radar and Multicast-Unicast Communication With Non-Orthogonal Multiple Access

In this work, we propose an effective approach to achieve robust covertness in joint radar and multicast-unicast communication using non-orthogonal multiple access (NOMA).Utilizing the same spectrum resource, a dual-functional radar-communication station covertly scans for unauthorized targets while receiving mixed multicast-unicast messages from a base station, including multicast information shared between radar and cell users and unicast covert information intended for cell users. Simultaneously, the unauthorized target monitors the radar's sensing activity to hide its existence before tracking cell users' unicast transmission covertly. NOMA power allocation is considered for both mixed multicast-unicast messages and the transmission between the radar and base station. In this context, we propose enhancing system covertness by first deriving exact closed-form expressions for the minimal detection error probability (DEP) of two-phase monitoring at the unauthorized target and jointly treating them as stringent constraints of system designs, along with the minimal communication rate requirements, when optimizing the power resources of the radar and base station to achieve the mutual information maximization of radar sensing activity. Through in-depth analysis of the DEP in conjunction with intelligent transformations using successive-convex approximation method, we can effectively obtain the near optimal power allocation solution, which is then thoroughly validated through numerical experiments.